Of manufacturing and the expectations of dimensional and geometric qualities that can be achieved. I have 1980s manufacturing magazines that brag about how "CNC technology can now maintain tolerances better than 0.010"". Forgive me if that's not impressive anymore. Technology moved on and we got worse.
Here's another example: supply a drawing and 3D model to manufacturing. They inexplicably screw up the location of basic mounting holes. Walk over and talk to them. Eventually get out of them that they were at the end of their shift so they broke down the machine and went home without the holes. They did them the next day. Stupid but, okay. Why didn't they indicate it back into the machine? "well, you didn't specify a tolerance and I can hit the +/- 0.020 in the title block without checking."
Was that lazy or stupid? The minute someone puts 3 place GD&T requirements, it gets sent off to the CMM and spends more time in inspection than they spent trying to figure out the crappiest way they could make it and squeak by.
Another: try to give manufacturing some breathing room by specifying wider flatness and parallelism zones on what should be a datum surface. The intent is to accept something that maybe twists during manufacturing but, will acceptably flex enough on assembly to not matter. There's maybe a center bored hole that has to be some squareness to the surface.
What we get back is something where they took advantage of the wide tolerance to hit the raw stock with a DA sander (because the zone was wide enough to include everything on that surface). Then they did a shitty bore job on a knee mill and barely made squareness because "your drawing allowed that and it meets the specification." Yes, but no. I didn't want a piece of crap to deliver to our customer.
These would be examples of not meeting "best shop practice". I agree that's an ambiguous note but, I don't know any other way to communicate: don't produce crap. It's the 21st century. Doing this in a CNC isn't a hardship.
Modern CNC equipment does not provide anything new or better in terms of geometric precision. Not in any meaningful way at least. Good quality 5 axis machines make it easier, but are not inherently more accurate than say an optical dual rotary table.
I still think you're missing the point. Maybe we work with different types of parts. It has nothing to do with CNC or how manufacturing capabilities have advanced. If a part has some critical multi-directional perpendicularity requirement between discreet features or a finite and quantifiable maximum cylindrical error of a round feature, that must be met or the part will not function, how do you define that on a drawing unambiguously? How does the machinist know that these things matter, if it cannot be assumed that the requirements will be met, regardless of how advanced the equipment is that they have to perform the work, unless it is specified with standardised methodology in a way that the machinist can understand and take whatever necessary precautions to ensure it?
I know that's verbose, but it's important. GD&T fills a very necessary role, and until someone can actually replace it with something better, it's what we've got.
I don't like GD&T any more than the next guy, but I understand why it's necessary and I personally don't have any objectively better ideas on how to perform its function.